COMPARISON OF ELECTRON-PARAMAGNETIC-RESONANCE LINE-SHAPES AND ELECTRON-SPIN RELAXATION RATES FOR C-60(-) AND C-60(3-) IN 4 1 TOLUENE-ACETONITRILE AND DIMETHYL-SULFOXIDE/

To assess the effect of solvent on the properties of C-60 anions, solu tions of C-60(-) and C-60(3-) were generated electrochemically in 4:1 toluene:acetonitrile or DMSO containing 0.1 M tetrabutylammonium hexaf luorophosphate. The anions were characterized by NIR spectroscopy and square-wave voltammetry. In both solvents continuous wave (CW) electro n paramagnetic resonance (EPR) spectra at 8 K are axial for C-60(-) an d rhombic for C-60(3-), consistent with increasing distortion of the a nion with increasing addition of electrons to the LUMO of C-60. The li ne shapes in the wings of the spectra, decreasing anisotropy of the sp ectra with increasing temperature, faster phase memory relaxation rate s in the wings of the spectra, and distribution of values of the spin- lattice relaxation rate (1/T-1) provide evidence for a distribution of Jahn-Teller distorted forms and increasing rates of interconversion b etween these forms with increasing temperature. These properties are s imilar in the two solvents, despite substantial differences in solvent polarity. Extrapolation of the temperature dependence of 1/T-1 measur ed below 30 K suggests that the line widths above 70 K are relaxation determined. Above about 70 K the line widths of the CW spectra broaden as increasing mobility of the solute/solvent increases the rate of sp in-lattice relaxation.